| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letters to the Editor |
Department of Angiology, Medical University Vienna, Währinger Gürtel 18–20, A-1097 Vienna, Austria. e-mail: erich.minar@meduniwien.ac.at
Editor:
We read with great interest the article of Dr Krueger and colleagues in the May 2004 issue of Radiology (1) in which the authors were able to demonstrate by means of repeated angiographic controls a significantly reduced degree of restenosis up to 24 months after angioplasty of de novo femoropopliteal lesions in patients who underwent endovascular irradiation. When compared with the number of clinical studies dealing with prevention of restenosis after coronary interventions, unfortunately there is a paucity of such randomized trials after femoropopliteal interventions.
While pharmacologic adjuncts and metallic stents did not improve the patency rate after femoropopliteal angioplasty in controlled trials, we demonstrated the effectiveness of endovascular irradiation as the first therapeutic modality, to our knowledge, able to achieve this goal in patients with a high risk of restenosis (2). Recently, further randomized trials have been performed in Europe with centered (3) and noncentered (4,5) endovascular gamma irradiation, all demonstrating a significant improvement of short- and midterm patency after angioplasty of restenotic or de novo femoropopliteal lesions. The small—however very elegantly performed—study of Dr Krueger and colleagues (1) gives further evidence for this therapeutic concept.
While the results of the pilot phase of the Peripheral Artery Radiation Investigational Study (PARIS)—the only trial of peripheral endovascular irradiation performed in the United States—have also been promising (6), the recently reported final results (7) were not different between the treatment and control groups with respect to clinical and angiographic end points. Despite the difficulties with patient recruitment and follow-up in PARIS, these negative results had the consequence to abolish peripheral endovascular irradiation by most interventionists in the United States. However, the data reported by Dr Krueger and colleagues (1) and the positive results of other European trials are a strong argument to pursue this concept in further studies. This is also supported by the current lack of an alternative, since—in contrast to the coronary arteries—drug-eluting stents are not an available alternative in the femoropopliteal region.
Since most interventionists were uncomfortable with the formerly used procedure of afterloading gamma irradiation because of logistic problems due to the special shielding requirements and because of the requirement of relatively large delivery systems, future studies in this field should focus on beta-emitting sources enabling treatment in the normal interventional radiology suite.
REFERENCES
Department of Radiology, University of Cologne, Joseph-Stelzmann-Strasse, Cologne D-50924, Germany. e-mail: karsten.krueger@uni-koeln.de
Before responding to their letter to the editor, we thank Drs Minar and Schillinger for their thoughtful comments and appreciate the attention that our work has received (1).
Drs Minar and Schillinger refer to some of the current issues involving the present value of endovascular gamma irradiation for the prevention of restenosis in the superficial femoral artery and popliteal artery. The PARIS study was unable to prove that the adjuvant use of endovascular gamma irradiation lowered the restenosis rate compared with that in the control group (2). Have the findings of the PARIS study now knocked endovascular brachytherapy out of the race to develop a method for reducing the frequency of restenosis? Unlike the PARIS trial, several published studies conducted in Europe (3–7) demonstrated that both centered and noncentered endovascular brachytherapy led to a significant reduction in the restenosis rate. This was true for de novo as well as recurrent stenoses of the femoral artery. Unfortunately, the results of the PARIS study have thus far only been published in the form of abstracts, encumbering any detailed critical appraisal of its findings.
Drs Minar and Schillinger do call attention, however, to an important problem associated with endovascular irradiation in peripheral vessels—the acceptance of the method by the international radiologic community, which has been hampered by two key factors. The first is the greater logistic outlay: To maintain radiation safety, gamma irradiation delivered in the dose required cannot be performed in the angiography suite. For afterloading, the patient then has to be moved to the radiation therapy suite. This prolongs the duration of the intervention and places higher demands on exacting coordination between radiation therapy physicians and physicists. Despite this added effort, the latter was not an issue in our study, although in general, it would indeed be desirable for brachytherapy to be performed directly in the catheter laboratory.
As Drs Minar and Schillinger discussed, beta sources are, in principle, suitable for this, since they are much easier to shield than gamma sources. A reduction in the restenosis rate can also be achieved with beta sources, as studies on coronary arteries have shown (8,9). However, no findings from clinical trials have been available to date on the effectiveness of beta-emitting sources in peripheral arteries. This is due to the principles of radiophysics. The dose from beta sources drops much more sharply than from gamma sources. On one hand, this is desirable because it ensures that only the vessel wall is irradiated. On the other hand, the dose delivered to the intima is higher than with gamma irradiation. Therefore, it is even more important to center the radiation source when beta emitters are used than when the radiation derives from a gamma source.
The catheter currently available for source centering (PARIS Centering Catheter System; Guidant, Temecula, Calif) has been associated with some disadvantages, which we believe is another reason for the low acceptance of endovascular brachytherapy. The use of the PARIS catheter requires an 8-F sheath. This makes the entire intervention more invasive. Centered irradiation with the cross-over approach is not always possible, depending on the vascular anatomy of the aortic bifurcation and the iliac arteries, and a second antegrade puncture may become necessary. Additionally, radiation source centering can carry a risk of thromboembolic complications (10). Technical improvements to the centering catheter would thus be desirable.
Finally, the question as to whether it is necessary to center the radiation source when administering brachytherapy with gamma irradiation from sources such as iridium 192 has not yet been answered. A radiation biologist would argue in favor of centering, yet clinical studies have shown that a reduction in the restenosis rate after percutaneous transluminal angioplasty of the femoral artery can also be achieved with a noncentered radiation source.
Are current alternatives to endovascular gamma irradiation for preventing restenosis in femoral arteries truly lacking? Clinical studies on sirolimus-coated stents have yielded very promising results for coronary arteries. For the treatment of coronary stenosis, authors of recent reports have discussed whether endovascular gamma irradiation has any more merit at all in light of the results obtained in drug-eluting stent trials. Drs Minar and Schillinger justly point out that such stents for use in peripheral arteries are (still?) currently not commercially available. The SIROCCO study (11) certainly demonstrated positive effects with sirolimus-coated stents in femoral arteries. In this connection, the relatively low in-stent mean percentage diameter stenosis of 30.9% achieved with noncoated stents over a period of 6 months is of interest (22.6% in the sirolimus-eluting stent group). Hence, the in-stent restenosis rate appears to be lower with more modern and more flexible stents than was shown in earlier studies (12).
To conclude, endovascular brachytherapy is currently the only treatment proved in several clinical studies to lead to a reduction in restenosis rate after percutaneous transluminal angioplasty of stenoses in femoropopliteal arteries and is generally available for clinical use. The rate of side effects is low. Acceptance of the method would improve if technical developments were made to the catheters used for irradiation and if the logistic outlay could be reduced with better shielded emitters. On the basis of current evidence from clinical trials, we believe that it would be premature to discard the concept of endovascular brachytherapy for restenosis prevention in femoral arteries.
REFERENCES
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOLOGY | RADIOGRAPHICS | RSNA JOURNALS ONLINE |
